The measurement of reticulated platelets, that is immature platelets, is considered to reflect the platelet production function in the marrow, and has been reported to be useful in differentiating idiopathic thrombocytopenic purpura (ITP) and other thrombopenic diseases (for example, aplastic anemia (AA)). Furthermore, the measurement of reticulated platelets has been reported to be useful as a platelet recovery index after chemotherapy and stem cell transplantation.
Conventional methods for measuring immature platelets typically produce an assay sample by reacting platelets in a blood specimen with an anti-platelet antibody treated with a fluorescent marker, and fluorescently staining the platelets with fluorescent dye, then measuring the platelets with a flow cytometer. This method takes a comparatively long time for the antigen-antibody reaction and fluorescent staining, and the work of producing the sample is complex.
An example of an automatic measuring apparatus providing a simpler method for measuring immature platelets is disclosed in U.S. Pat. No. 6,133,995. It describes a device in which olamin-O, a fluorescent dye that bonds with cellular RNA, is used to fluorescently stain platelets in the blood, the fluorescently stained blood sample flows through a flow cell, and the particles in the blood sample flowing through the flow cell are irradiated by an argon ion laser beam, then the scattered light and fluorescent light generated from each particle are detected and analyzed to differentiate and count the reticulated platelets.
An argon ion laser light source is used in the device disclosed in U.S. Pat. No. 6,133,995. However, the argon ion laser light source is extremely expensive. Furthermore, the entire device is made larger in scale because the argon ion laser light source is large. However, the olamin-O and other usable materials disclosed in the same publication, that is, acridine orange, propidium iodide, ethidium bromide, Hoechst 33342, pyronin Y, and rhodamine 123 used in the device disclosed in the embodiments in U.S. Pat. No. 6,133,995 are invariably fluorescent dyes which emit fluorescent light when excited by the wavelength of an argon ion laser. Therefore, when semiconductor laser light sources having a different excitation wavelength is used, it is difficult to measure the reticulated platelets using the various fluorescent dyes.